1. Field of the Invention
The present invention generally relates to golf balls and, more particularly to golf balls having an improved arrangement of dimples thereon.
2. Description of the Prior Art
Heretofore, a lot of improvements or reforms have been proposed, and some of which have been actually put into practice, with respect to the pattern and the dimension of dimples formed on the surface of golf balls, mainly for the purpose of improving flight characteristics of the golf balls.
Broadly classifying the known techniques for forming the improved golf balls, there are such ones as disclosed, for example, in Japanese Patent Publication (Unexamined) Tokkaisho No. 60-96272 and Japanese Patent Publication (Unexamined) Tokkaisho No. 58-25180, wherein the dimension of the dimples, all of which are uniformly formed, that is, the diameter, the depth, the cross section, etc. are tried to be optimum, in Japanese Patent Publication (Examined) Tokkaisho No. 58-50774 and Japanese Patent Publication (Unexamined) Tokkaisho No. 53-115330 wherein the pitch between the two adjacent dimples is set within a given range, and in Japanese Patent Publication (Unexamined) No. 57-107170 according to which all of the dimples are arranged with an equal pitch to each other.
All of the above-described known techniques are commonly based on the premise that all the dimples formed on the surface of a golf ball have the same uniform dimension. This is because of the general conception that the roughness on the spherical surface of the golf ball affects the force of air as the average dimension since the golf ball travels at a high speed of 40-80 m/sec and with a revolution of 2000-10000 rpm in tournament play.
In the meantime, the dimples on the golf ball play the role for accelerating the transition of the disturbed flow of the air in the boundary layer so as to separate the disturbed flow of the air off the golf ball. Accordingly, a golf ball with dimples, in comparison with one without dimples, can be made such that a point of separation is brought further backwards and the separation area is reduced, which in turn leads to the reduction of pressure resistance and the improvement of lift owing to the promotive difference between the upper and the lower separation points. Moreover, the dimples should work all around either when the golf ball travels at lower speeds or when the golf ball travels at high speeds.
However, in a conventional golf ball, for example, as shown in FIG. 9 which is arranged with the dimples (a) each having the same shape and the same size, the air flows in a different way at every position on the surface of the golf ball. More specifically, the flow of the air at the cross sections (e--e), (f--f), (g--g), etc. crossing at right angles with respect to the rotational axis (b) of the ball interferes with each other. Therefore, it might be considered that the dimples work less effectively. In other words, during the travelling of the golf ball in the direction H, the position of each separation points E, F and G respectively at cross sections (e--e), (f--f), (g--g) changes greatly because of the great difference in degrees of the roughness in each cross section, and accordingly, the flow of the air at the cross section (f--f) hinders the flow of the air at the cross section (e--e) and that at the cross section (g--g), thereby deteriorating the effective function of the dimples. On the other hand, the flow of the air at each of the cross sections (e--e), (f--f) and (g--g) is inclined itself to be stabilized and settled in accordance with the dimension of the dimples, which inclination would be due until the golf ball falls down on the ground after it is shot.
Therefore, even when the pattern, the pitch, etc. of the dimples all having the same dimension as shown in FIG. 9 are tried in various ways so as to be optimum, the dimples cannot be effective.
Meanwhile, considering the pattern of the arrangement of the dimples, it is necessary to be non-directional as much as possible, and various proposals have been made for the arrangement pattern of the dimples.
Namely, a first proposal is a golf ball having about 336 dimples arranged in a regular octahedron such as disclosed in Japanese Patent Publication (Unexamined) Tokkaisho No. 60-111665, which has 416 dimples impressed thereon. A second proposal is a golf ball having 360 dimples arranged in the form of regular dodecahedrons. A third proposal is a golf ball having 252 dimples arranged in the form of an affine icosahedron, as is disclosed in Japanese Patent Publication (Unexamined) Tokkaisho No. 49-52029, or a golf ball having 492 dimples impressed therein. Fourthly proposed is a golf ball as is disclosed in Japanese Patent Publication (Unexamined) Tokkaisho No. 58-50744, which has approximately 332 dimples or 392 dimples by the reduction or addition of one row of the seam portion of dimples from or to the arrangement in the form of an icosahedron for the convenience of the molding technique. And, such a golf ball as is disclosed in Japanese Patent Publication (Unexamined) Tokkaisho No. 53-115330 and having about 280-350 dimples arranged in concentric circles is fifthly proposed. A sixth proposal is a golf ball with 320 dimples arranged with an equal pitch between the two adjacent dimples as is disclosed in Japanese Patent Publication (Unexamined) Tokkaisho No. 57-107170.
The arrangement of patterns of the dimples in the above-described proposed, except in the first, second and sixth proposals, are all strongly directional. What is worse, the trajectory differs depending on the rotational axis at the time when the golf ball is shot, and therefore, these proposals, except the first, second and sixth proposals, should be out of the question in view of the non-directionality.
On the other hand, so long as the non-directionality is aimed, the arrangement of the dimples in the form of regular dodecahedrons, regular octahedron are proper, as well as the arrangement in the form of a regular tetrahedron, that in the form of a cube, or in the form of regular icosahedrons, because they are basically the arrangement in the form of a regular polyhedron.
As referred to earlier, the mold of the golf ball is made of two recessed hemispheres. On the seam of the two hemispheres, the dimples cannot be formed.
Accordingly, in view of the foregoing circumstances, only the arrangement in the form of a regular octahedron can be employed for the non-directional arrangement of the dimples (among the five arrangements).
Semi-regular polyhedrons can be also taken into consideration as one example of a polyhedron having edges of the same length. Although there are thirteen semi-regular polyhedrons, only the cubic octahedron and icosa-dodeca hedrons are able to be cut into two pieces, without the circumscribed sphere thereof passing through the planes and, at the planes including only the edges. The cubic octahedron has fourteen planes and the icosa-dodeca hedrons have thirty-two planes. While noting the fact that the number of dimples in a standard golf ball ranges from 250 to 550, it is found that the arrangement in the form of icosa-dodeca hedrons is most suitable for easily realizing the non-directional arrangement.
Although the arrangement in the form of a geodesic polyhedron as described in Japanese Patent Publication (Unexamined) Tokkaisho No. 57-107170 is most promising from the viewpoint of the non-directionality, the number of the dimples able to be impressed in the golf ball is limited to 320, 720, etc. according to this arrangement, and therefore, this arrangement is inconvenient in that the number of the dimples cannot be freely changed. As will be described later, it is most important to change the number of dimples in accordance with the structure of the golf ball or the size of the golf ball in order to make optimum the trajectory of the golf ball and the flight distance. Thus, it can be so decided that the arrangement in the form of icosa-dodeca hedrons is most preferable.
There are considered various kinds of arrangements for the dimples in the form of icosa-dodeca hedrons. However, supposing that the number of the dimples at the five-cornered portions is p, and the number of the dimples at the three-cornered portions is t, the total number N of the dimples is expressed by an equation N=12p+20t.
For example, in the case where p is 26 and t is 6, the total number N of the dimples is 432.
One example of how 432 uniform dimples are arranged is shown in FIG. 10.
As stated earlier, the arrangement in the form of icosa-dodeca hedrons is employed with the aim towards the non-directionality in the arrangement. However, even in the arrangement in the form of icosa-dodeca hedrons when the same and uniform dimples are used, discrepancies occur in the position of the separation points E, F and G from each other as shown in FIG. 10, in the same manner as in FIG. 9, resulting in poor stability of the separation points during the travel of the golf ball. The dimples become less effective.
Accordingly, it will be deemed that even with the employment of a good arrangement of the dimples, the dimples all with the same dimension impressed on the surface of the golf ball cannot realize full effect.